One of the conventional methods of rapidly determining whether an unconscious person is alive is to check for the existance of breathing. At times this may be done under hospital conditions. At other times, such as at the site of armed conflicts, disasters or accidents, it must be done in the field.
Direct detection of breathing is unreliable because the respiration of an injured or ill person may be sporadic, irregular or so subtle as to be nearly imperceptible. Accordingly, medical science abounds with complex technology that detects, monitors and measures respiration.
There are many devices commonly in practice. One device used to detect breathing is a thermistor or thermocouple placed in or near the patient's airway so that the patient's breath passes over the temperature sensing device. Breathing gas entering the patient has a temperature that is generally lower than the exhaled gas.
A second device for measuring the airflow to and from a patient is a pneumotach sensor placed between a supply of breathing gas and the patient's airway. The pneumotach provides a known resistance to the flow. The patient's breathing capacity may increase the resistance, which is measured.
A third type of airflow meter is a nasal cannula meter which includes a pair of ports that insert into the nares of the patient. A hollow tubing carries a fraction of the total amount of breathing gas to a sensor. If the total area of the patient's nares relative to the total area of the ports is known, the meter can provide a quantitative measure of the patient's airflow.
A fourth method uses a microphone or pressure sensor mounted on the exterior of the patient's neck to detect sounds or throat vibrations generated by respiration.
A fifth method is to convert air flow to an oscillatory wave signal and measure its amplitude. See, for example, devices recently taught by Berthon Jones in U.S. Pat. Nos. 5,704,345, 6,029,665 and 6,138,675.
Other devices found for monitoring or measuring breathing include those in which the air flow mechanically rotates a propeller, displaces a vane, causes rotation of a tube or moves a ball within a tube, each of which is measured and provides an indication of the respiratory function of the subject.
Prior art reflects many devices for monitoring breathing that rely on pressure measurement to evaluate respiratory function. In U.S. Pat. No. 5,970,801, Ciobanu, et al disclose a variable orifice flow sensor that measures air flow by use of a hinged flapper which deflects as a result of air flow and triggers pressure sensing taps.
Starr et al, in U.S. Pat. No. 6,017,315, shows a monitor for measuring respiration that uses a pressure sensitive sensor.
In U.S. Pat. No. 5,052,400, Dietz discloses a method and apparatus that detects breathing by means of a pressure capacitance transducer that develops pressure variations in response to breathing.
Riker, in U.S. Pat. No. 5,170,798, teaches a pulmonary function tester that uses a pressure transducer in the mouthpiece to measure ambient pressure prior to and after sensing the pressure created by a patient's pulmonary function.
As can be seen from the above, all of the devices in use for monitoring breathing do more than merely indicate the existence of respiration. Rather, each of them uses a complex sensing device to detect, monitor or measure respiration. Moreover, all of the devices and methods referred to above require complex and expensive machinery that is typically found only in medical facilities. Such devices are not customarily brought into the field and most certainly not to remote or rugged sites.
There does not exist a simple and portable mechanical device that reliably detects and displays the existence of breathing, particularly at very low levels, without relying upon relatively complex technology to do so.